1. Technical Field
The present method relates to a method of treating hyperpigmentation in black skin with retinoic acid and a method of lightening black skin with retinoic acid.
2. Background Art
Post inflammatory hyperpigmentation (PIH) presents as irregular, darkly-pigmented spots occurring after inflammation due to an injury to the skin from an insult such as acne, folliculitis, eczema, or shaving. PIH resolves slowly but may persist for months. Black (e.g., Negroid) subjects of all ages are commonly afflicted with PIH, and the consequent disfigurement may necessitate medical attention (J. A. Kenney, Jr., et al., Clinics in Dermatology, 1989; 7:1-10; P. E. Grimes et al., Dermatologic Clinics, 1988; 6:271-81; and C. J. McDonald et al., Progress in Dermatology, 1979, 4:15-20). Although the biology of skin pigmentation is relatively well-understood, therapy for PIH is unsatisfactory and currently available therapies, such as the use of hydroquinones as bleaching agents, can result in unsightly depigmentation, irritant dermatitis, and ochronosis (C. J. McDonald, Prog. in Dermatol., 1973; 4:15-20; Kligman A. M. et al., Arch. Dermatol., 1975; 111:40-48; G. H. Findlay et al., Br. J. Dermatol., (1975) 93:613-22; and R. A. Hashaw et al., Arch. Dermatol., (1985) 121:105-8). Exemplary of such therapies is one described by Nair et al. (EP-A1-421,110) in which 4-hydroxyanisole (a hydroquinone derivative) and a retinoid are topically administered to treat hyperpigmentation associated with freckles, senile lentigo, lentigines, melasma, PIH, sunburn, and phototoxic reactions; from the Nair et al. disclosure the retinoid appears to be present because it is disclosed as decreasing the thickness of the stratum corneum and thus possibly facilitating the penetration of topically-administered bleaching agents (though the decrease occurs over time).
In recent studies on the use of topically applied retinoic acid (RA) for the treatment of photodamaged skin, lightening of sun-induced dyspigmentation, i.e., actinic lentigines, has been observed (J. S. Weiss et al., JAMA, 259:527-32 (1988); A. M. Kligman et al., J. Am. Acad. Dermatol., 15:836-59 (1986); G. D. Weinstein et al., Arch. Denmatol., 127:659-65 (1991); E. S. Rafal et al., New Engl. J. Med., 326:368-374 (1992); C. N. Ellis et al., J. Am. Acad. Dennatol., 23:629-37 (1990); and E. A. Olsen et al., J. Am. A cad. Dermatol., 26:215-24 (1992)). Sun-induced dyspigmentation is a heterogeneous entity in whites (E. S. Rafal et al., New Engl. J. Med., 326:368-374 (1992)) which may share features of melanin deposition with PIH. RA has not been used previously for PIH because it was thought to cause, rather than ameliorate, hyperpigmentation, and to be poorly tolerated (C. J. McDonald et al., Prog. in Dermatol., 4:15-20 (1992)). Topical RA treatment has also been reported as effective for the treatment of liver spots associated with photodamage (E. S. Rafal et al., New Engl. J. Med., 326:368-74 (1992)).
A need remains in the art for a method of treating post-inflammatory hyperpigmentation. In addition, a method of lightening black skin would also be desirable.